The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
In commit 4c7da06f5a ("dm persistent data: eliminate unnecessary
return values"), r value in exit_ro_spine will not change, so
exit_ro_spine doesn't need a return value.
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
dm_bm_unlock and dm_tm_unlock return an integer value but the returned
value is always 0. The calling code sometimes checks the return value
and sometimes doesn't.
Eliminate these unnecessary return values and also the checks for them.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
When using nested btrees, the top leaves of the top levels contain
block addresses for the root of the next tree down. If we shadow a
shared leaf node the leaf values (sub tree roots) should be incremented
accordingly.
This is only an issue if there is metadata sharing in the top levels.
Which only occurs if metadata snapshots are being used (as is possible
with dm-thinp). And could result in a block from the thinp metadata
snap being reused early, thus corrupting the thinp metadata snap.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
The walk code was using a 'ro_spine' to hold it's locked btree nodes.
But this data structure is designed for the rolling lock scheme, and
as such automatically unlocks blocks that are two steps up the call
chain. This is not suitable for the simple recursive walk algorithm,
which retraces its steps.
This code is only used by the persistent array code, which in turn is
only used by dm-cache. In order to trigger it you need to have a
mapping tree that is more than 2 levels deep; which equates to 8-16
million cache blocks. For instance a 4T ssd with a very small block
size of 32k only just triggers this bug.
The fix just places the locked blocks on the stack, and stops using
the ro_spine altogether.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Add dm_btree_walk to iterate through the contents of a btree.
This will be used by the dm cache target.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This patch fixes a compilation failure on sparc32 by renaming struct node.
struct node is already defined in include/linux/node.h. On sparc32, it
happens to be included through other dependencies and persistent-data
doesn't compile because of conflicting declarations.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Now that the value_size is held within every node of the btrees we can
remove this argument from value_ptr().
For the last few months a BUG_ON has been checking this argument is
the same as that held in the node. No issues were reported. So this
is a safe change.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
The persistent-data library offers a re-usable framework for the storage
and management of on-disk metadata in device-mapper targets.
It's used by the thin-provisioning target in the next patch and in an
upcoming hierarchical storage target.
For further information, please read
Documentation/device-mapper/persistent-data.txt
Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
